The prevention of fouling by barnacles and other fouling genera commonly present in sea water, particularly on ship hulls and other marine applications including buoys, pier pilings, oil well rigs, undersea pipelines and the like is a continuing problem. In recent years some success has been obtained by the use of certain organo-tin compounds in certain elastomers which are not degraded or the physical properties substantially impaired by the presence of the organo-tin compound. Types of these applications are described in U.S. Pat. No. 3,426,473 wherein coverings resistant to marine fouling organisms are prepared from vulcanized natural rubber, neoprene, butyl rubber or nitrilebutadiene rubbers that contain bis-(tri-n-butyl tin-oxide). Typical applications for use, for example, in sonar bow domes are very labor intensive and the installation involves the hand lay up of quarter inch plies of green neoprene stock in amounts up to 8 inches in thickness, after which the dome must be transferred to a curing oven. This is an awkward operation since the amount of neoprene rubber used per dome is many thousands of pounds. Attempts to use polyurethanes, which may be applied in solid layers, or more preferably by casting, have been unsuccessful because bis(tri-n-butyl tin-oxide) severely degrades the polyurethane.